Nimodipine prevents memory impairment caused by nitroglycerin-induced hypotension in adult mice

Orexin one receptors within the basolateral amygdala are involved in the modulation of cognitive deficits associated with a migraine-like state in rats

OBJECTIVES

This study explored the possible role of orexin one receptors (Orx1R) in the basolateral amygdala (BLA) on the modulation of nitroglycerin (NTG)-induced migraine-like symptoms. In addition, pain-induced subsequent alteration in learning and memory competence was evaluated in the adult male Wistar rats.

METHODS

The rats were given NTG (5 mg/kg, i.p.) every two days (for nine-day) to induce a migraine-like state. The migraine animals were treated with intra-BLA infusion of an Orx1R antagonist SB 334,867 (10, 20, and 40 nM/rat) or its vehicle DMSO. The NTG-induced migraine symptoms were recorded for 90 min. Spatial and passive avoidance performances were assessed by Morris water maze (MWM) and shuttle box tasks, respectively.

RESULTS

In comparison with control, NTG produced significant migraine-like symptoms characterized by a decrease in cage climbing and an increase in head-scratching, freezing, and facial grooming behavior. Intra-BLA infusion of SB 334,867 (40 nM/rat) significantly decreased cage climbing and increased facial grooming responses in NTG-treated rats. Moreover, all administrated doses of SB 334,867 increased NTG-evoked head-scratching and freezing behavior. Besides, NTG impaired learning and memory performances in both tests, which were exaggerated by post-injection of SB 334,867 (40 nM/rat).

CONCLUSIONS

Overall, the data provided an emerging role for the orexin system within BLA in the modulation of cognitive decline comorbid with migraine in rats.

Isoflurane prevents learning deficiencies caused by brief hypoxia and hypotension in adult Sprague Dawley rats

CONTEXT

Hypotension causes histologic changes in the hippocampal CA1 area, while behavior remains unchanged. We believe that an even stronger insult may also cause behavioral changes.

OBJECTIVE

We used a rat hemorrhagic shock model plus temporary hypoxia to assess functional outcome at different time points post-injury. Our hypothesis is that the damage can be attenuated by the use of isoflurane.

MATERIALS AND METHODS

Rats were subjected to brief hypotension. Animals were evaluated at different time points after receiving hypoxia and hypotension, with and without isoflurane treatment.

RESULTS

The administration of isoflurane after the insult protected the animals from memory alterations. No histopatologic changes were found in any of the groups.

DISCUSSION AND CONCLUSIONS

This observation suggests that in this model of hypotension plus hypoxia there is mild cerebral damage that is reflected by memory changes. Exposure to isoflurane after the insult can prevent the onset of memory deficits.

Small molecule inhibitors in the treatment of cerebral ischemia

INTRODUCTION

Stroke is the world's second leading cause of death. Although recombinant tissue plasminogen activator is an effective treatment for cerebral ischemia, its limitations and ischemic stroke's complex pathophysiology dictate an increased need for the development of new therapeutic interventions. Small molecule inhibitors (SMIs) have the potential to be used as novel therapeutic modalities for stroke, since many preclinical and clinical trials have established their neuroprotective capabilities.

AREAS COVERED

This paper provides a summary of the pathophysiology of stroke as well as clinical and preclinical evaluations of SMIs as therapeutic interventions for cerebral ischemia. Cerebral ischemia is broken down into four mechanisms in this article: thrombosis, ischemic insult, mitochondrial injury and immune response. Insight is provided into preclinical and current clinical assessments of SMIs targeting each mechanism as well as a summary of reported results.

EXPERT OPINION

Many studies demonstrated that pre- or post-treatment with certain SMIs significantly ameliorated adverse effects from stroke. Although some of these promising SMIs moved on to clinical trials, they generally failed, possibly due to the poor translation of preclinical to clinical experiments. Yet, there are many steps being taken to improve the quality of experimental research and translation to clinical trials.

Hippocampal cellular loss after brief hypotension

Brief episodes of hypotension have been shown to cause acute brain damage in animal models. We used a rat hemorrhagic shock model to assess functional outcome and to measure the relative neuronal damage at 1, 4 and 14 days post-injury (3 min of hypotension). All rats underwent a neurological assessment including motor abilities, sensory system evaluation and retrograde memory at post-hypotensive insult. Brains were harvested and stained for Fluorojade C and Nissl. Stereology was used to analyze Fluorojade C and Nissl stained brain sections to quantitatively detect neuronal damage after the hypotensive insult. Statistical analysis was performed using Graphpad Prism 5 with the Bonferroni test at a 95% confidence interval after ANOVA. A Mixed Effect Model was used for the passive avoidance evaluation. Stereologically counted fluorojade positive cells in the hippocampus revealed significant differences in neuronal cell injury between control rats and rats that received 3 min of hypotension one day after insult. Quantification of Nissl positive neuronal cells showed a significant decrease in the number hippocampal cells at day 14. No changes in frontal cortical cells were evident at any time, no significative changes in neurological assessments as well. Our observations show that brief periods of hemorrhage-induced hypotension actually result in neuronal cell damage in Sprague–Dawley rats even if the extent of neuronal damage that was incurred was not significant enough to cause changes in motor or sensory behavior.

Nimodipine improves regional cerebral blood flow and suppresses inflammatory factors in the hippocampus of rats with vascular dementia

OBJECTIVE

To study the effect of nimodipine on hippocampal regional cerebral blood flow (rCBF) and proinflammatory cytokines in rats with experimental vascular dementia.

METHODS

Male Sprague Dawley rats were randomly divided into four groups (n = 15/group): sham operated controls (group A); focal cerebral ischaemia (group B); vascular dementia (group C); and vascular dementia treated with 20 mg/kg nimodipine daily (group D). The Morris water maze test evaluated learning and memory, and magnetic resonance perfusion-weighted imaging was used to measure rCBF. Hippocampal levels of nuclear factor-κB (NF-κB), tumour necrosis factor-α (TNF-α) and interleukin 1β (IL-1β) were measured.

RESULTS

Compared with group C, rats in group D demonstrated significantly improved learning ability and significantly increased hippocampal rCBF. The levels of NF-κB, TNF-α and IL-1β were significantly lower in group D than in group C. Hippocampal nerve cell morphology was abnormal in group C but near normal in group D.

CONCLUSIONS

Nimodipine improved the symptoms of cognitive impairment, increased rCBF, reduced hippocampal cytokine levels and alleviated neuronal injury in the hippocampus of rats with experimental vascular dementia.

Nimodipine-induced hypotension but not nitroglycerin-induced hypotension preserves long- and short-term memory in adult mice

BACKGROUND

Acute hypotension may be implicated in cognitive dysfunction. L-type calcium channel blockers in the setting of hypoxia are protective of learning and memory. We tested the hypothesis that hypotension induced by nimodipine (NIMO) and nicardipine (NICA) would be protective of long- and short-term memory compared to hypotension induced by nitroglycerin (NTG).

METHODS

Forty Swiss-Webster mice (30 to 35 g, 6 to 8 weeks) were randomized into 4 groups for i.p. injection immediately after passive avoidance (PA) learning on day 0: (1) NTG (30 mg/kg); (2) NICA (40 mg/kg); (3) NIMO (40 mg/kg); and (4) saline. PA training latencies (seconds) were recorded for entry from a suspended platform into a Plexiglas tube where a shock (0.3 mA; 2-second duration) was automatically delivered. On day 2 latencies were recorded during a testing trial during which no shock was delivered. Latencies >900 seconds were assigned this value. Lower testing latency is indicative of an impairment of long-term associative memory. Forty-nine additional mice were randomized into similar groups for object recognition testing (ORT) and given i.p. injections on day 0. ORT measures short-term memory by exploiting the tendency of mice to prefer novel objects where a familiar object is present. On day 5 during training, 2 identical objects were placed in a circular arena and mice explored both for 15 minutes. A testing trial was conducted 1 hour later for 3 minutes after a novel object replaced a familiar one. Mice with intact memory spend about 65% of the time exploring the novel object. Mice with impaired memory devote equal time to each object. Recognition index (RI) is defined as the ratio of time spent exploring the novel object to time spent exploring both objects was the measure of memory. Mean arterial blood pressure (MAP), cerebral bloodflow, and body and brain oxygenation (PO(2)) studies were done in separate groups of mice to determine the dosages for matched degrees of hypotension and the physiological profile of each treatment.

RESULTS

The median PA latencies for the different conditions were as follows: NTG (219.5 ± 93.5 second semi-interquartile range [SIQR]), NICA (372.5 ± 75.5 second SIQR), NIMO (540 ± 200 second SIQR) and saline (804 ± 257.5 second SIQR). Rank methods were used to analyze the PA latencies for significant differences. NTG latency was significantly shorter than NIMO latency (P = 0.012) and saline latency (P = 0.006), but not NICA latency (P = 0.126). ORT RI values showed a similar pattern. We found that NTG RI (47.2 ± 5.9% SEM) was different from NIMO RI (60.2 ± 4.6% SEM, P = 0.031) and different from saline RI (66.9 + 3.7% SEM, P = 0.006). Physiological experiments showed that MAP decreased to 45 to 50 mm Hg in all animals who became minimally responsive to external stimuli within 10 to 15 minutes of injection. Intergroup differences for MAP, body and brain oxygenation, and cerebral bloodflow were not statistically significant.

CONCLUSION

Acute hypotension induced by NIMO was protective of 2 categories of memory formation relevant to the clinical posttreatment period. Both immediate long-term associative memory consolidation as measured by the PA learning paradigm and delayed short-term working memory function as measured by the ORT paradigm were significantly improved compared to matched levels of hypotension induced by NTG. These results indicate the utility of further investigation of l-type calcium channel blockers as a potential means of preserving cognition in the setting of hypotensive and low flow states.

Sevoflurane impairs memory consolidation in rats, possibly through inhibiting phosphorylation of glycogen synthase kinase-3β in the hippocampus

Sevoflurane administration impairs memory processes in both humans and animals. Increasing evidence suggests that enhancement of the phosphorylation state of glycogen synthase kinase-3β (GSK-3β), as a result of acute administration of lithium chloride (LiCl), may enhance memory consolidation. The current experiments examined whether GSK-3β phosphorylation was involved in mediating the memory impairing effects of posttraining sevoflurane on inhibitory avoidance (IA) retention. In experiment 1, adult male Sprague-Dawley rats were exposed to sevoflurane (0.5%, 1%, or 2%) for 2h immediately after training in a continuous multiple-trail IA paradigm. Sevoflurane (2% inspired) induced significant impairment of retention performance on a 24-h test and inhibited phosphorylation of GSK-3β in the hippocampus 2h after training. In experiment 2, administration of LiCl (100mg/kg, intraperitoneally) 30 min before IA training not only blocked the sevoflurane-induced impairment of consolidation, but also reversed the inhibitory effect of sevoflurane on GSK-3β phosphorylation in the hippocampus. Collectively, these findings support the hypothesis that sevoflurane exposure can impair consolidation of IA memory in rats. Sevoflurane-induced amnesia may be due, at least in part, to suppression of GSK-3β phosphorylation in the hippocampus.